Analysis of GPS Timer (NTP Satellite Timing Server) Scenario Application Technology Analysis of
GPS Timer (NTP Satellite Timing Server) Scenario Application Technology Analysis
In the field of communication, the concept of "synchronization" refers to frequency synchronization, that is, the clock frequency and phase synchronization of each node in the network, and its error should meet the requirements of relevant standards. At present, in the communication network, the frequency and phase synchronization problems have been basically solved, but the time synchronization has not been well resolved.
Time synchronization refers to the synchronization of the time and time interval of the clocks of each node in the network and the clocks of each application interface connected through the network with the Coordinated Universal Time (UTC), at least in a local or metropolitan area network to synchronize with Beijing time. The time synchronization network is the basis for ensuring time synchronization. The time synchronization network can be formed in a wired or wireless manner. Here we mainly introduce Internet time synchronization technology and products, that is, network time synchronization is realized through a network time server supporting the NTP protocol.
The basic unit of time is the second, which is one of the seven basic units of the International System of Units (SI Units). The International Conference on Weights and Measures (CGDM) in 1967 gave a new definition of the second: "A second is 9 192 631 770 cycles of the radiation corresponding to the transition between the two hyperfine energy levels of the ground state of cesium 133 (133Cs) at 0K temperature duration", or "atomic second" (TAI). Coordinated Universal Time in common use today is actually an atomic second adjusted for leap seconds.
At present, cesium atomic clocks are mainly used at the international and national reference levels. The frequency reproducibility of the cold atomic fountain cesium atomic clock established by the China Institute of Metrology is 5×10-15, which is close to the international advanced level. In fact, at the application level, such high time and frequency accuracy as the national benchmark is not required.
Different applications have different requirements for accuracy. Table 1 lists the requirements for time accuracy of some typical applications (the error of application interface time relative to UTC time).
Table 1: Application of time precision in some typical applications
Application time precision requirements
Computers and servers for banking, securities, stock and futures trading 1 second
Power line fault diagnosis 1 microsecond
Exchange and billing system 1 second
CDMA2000 and TD-SCDMA 10 milliseconds
Network management system 500 milliseconds
No. 7 signaling monitoring system 1 millisecond
At present, there are many time synchronization technologies, and each technology has its own characteristics. There are also large differences in the time synchronization accuracy of different technologies, as shown in Table 2:
Table 2: Various commonly used time synchronization technologies
Time synchronization technology accuracy coverage
Short-wave timing 1-10 milliseconds global
Long-wave timing 1 milliseconds Regional
GPS 5-500 nanoseconds global
Telephone dial-up timing 100 milliseconds Global
Internet timing (NTP) 1-50 millisecond global
SDH transmission network timing 100 nanosecond long-distance